1. Field of the Invention
This invention relates to a disc recording/reproducing apparatus for recording/reproducing signals to/from a disc-shaped recording medium, such as a magnetic disc, a magneto-optical disc or an optical disc.
2. Description of the Related Art
Referring to FIG. 1, a disc-shaped recording medium 65 may be exemplified by a magnetic disc, an optical disc, a magneto-optical disc or the like. The disc-shaped recording medium 65 has a preformatted region, in which data for producing tracking error signals or the address information indicating data positions on the disc are formed as a servo pattern at pre-set intervals, and a data region for recording data or reproducing the recorded data.
When the disc-shaped recording medium is rotated, minute movements of the center position of the recording medium, referred to herein as eccentricities, are produced as a result of chucking errors and pattern molding errors.
When tracking a recording/reproducing head 64 for reproducing data recorded on the disc-shaped recording medium 65 to a pre-set track on the recording medium, a target position signal indicating the pre-set track position is inputted to an additive node 61 which then adds a position detection signal to the target position signal. An output of the additive node is converted by a controller 62 and fed to a voice coil motor (VCM) 63 which is a driving means for minutely controlling the position of a recording/reproducing head 64 for maintaining the position of the pre-set track. The VCM 63 finely controls the position of the recording/reproducing head 64 to effect accurate tracking with respect to the pre-set track.
Playback signals from a disc 65 by the recording/reproducing head 64 are provided externally and are simultaneously supplied to a position detection unit 66. The position detection unit 66 detects an actual position of the recording/reproducing head and routes the detected head position as a position detection signal to the additive node 61.
When the recording/reproducing head 64 is to be set to stand-by state in the above-described disc recording/reproducing apparatus, the disc 65 is tracked to a pre-set track and halted at this stand-by position. However, due to the eccentricities, as described above, the center of a track circle may not be coincident with the center of rotation of the disc. Thus, it is necessary for the recording/reproducing head 64 to halt the head at the standby position while occasionally changing the distance between the head and the center of rotation of the disc. As a result, since the VCM is driven at all times with an offset frequency signal, a larger quantity of the electric current is wastefully consumed.
In addition, when measuring the frequency characteristics of the VCM while the recording/reproducing head is maintained on the pre-set track in the stand-by position, measurement is made in such a state wherein a bearing unit of the recording/reproducing head is offset by an amount corresponding to the eccentricity of the disc. As a result, it is not possible to measure minute amplitude characteristics of the VCM in the low frequency range.